1. Field of the Invention
This invention relates to an optical axis correction lens device that may be employed advantageously in an optical system for a hand-held type video camera and, more particularly, to a device for compensating the adverse effects of shaking and oscillations in such hand-held video camera.
2. Description of the Background
The hand-held video camera, provided with a so-called CCD image sensor, is now becoming quite popular. The hand-held video camera, however, has a drawback that because it is small-sized and lightweight it easily undergoes small positional deviations caused by fine oscillations of the user's hand during the pickup and recording of an image. In such case, when an image is picked up using a zoom lens, the reproduced image is subject to fine "wobbling" and hence presents difficulties when subsequently viewing the recorded, zoomed image.
Although these deviations may be prevented from occurring by securing the video camera device on a tripod during the image pickup and recording, this involves an extremely laborious operation and detracts from high operability of the portable, hand-held video camera.
There are known some techniques for correcting or compensating the positional deviations of the video camera. Such known techniques of correcting the deviations on the side of the video camera may be classified into systems that detect the deviations by picture processing based on movements of an object and systems that detect movements of the main body of the video camera by a deviation sensor and that directly detect an angular velocity of the deviations.
The former system for correcting deviations of the camera device held by the user's hand by picture processing lends itself to construction on an IC chip and, hence, to a reduction in size of the video camera, because picture signals produced on picking up the image of an object are processed into corresponding data. In such picture processing system, when the deviations of the camera device caused by fine oscillations of the user's hand are detected, part of the raster-like picture imaged on the CCD image sensor is taken out and moved in accordance with the picture of a previous field, until coincidence or a steady state is reached. In such case, the partial picture thus taken out is enlarged to an original picture size so as to be recorded on a video tape. This leads to an inconvenience that not only is the resolution lowered, because the original information is displayed only partially on the screen, but also the deviations of the camera device caused by fine movements of the user's hand can be corrected only within a limited range. Besides, if the object is moving in a fashion similar to the movements produced by the deviations of the hand-held camera, these object movements are apt to be mistaken for deviations of the camera and unintentionally removed or compensated. In addition, in places with poor illumination or weak ambient light, the movements of the object and hence the deviations of the hand-held video camera caused by fine movements of the user's hand occasionally cannot be detected.
On the other hand, a gimbal mechanical system has been known as constituting the latter system for optically correcting the deviations of the camera device caused by fine movements of the user's hand. This gimbal mechanical system, which involves moving the entire lens unit in a direction for canceling the deviations of the camera caused by shaking of the user's hand does not cause deterioration in resolution and permits correction over a broader range. Nevertheless, because the entire lens unit is moved, the overall camera system is increased in size while leading to a considerable increase in power consumption.
Thus, the above two proposed shake compensations systems each have their merits and demerits and, hence, cannot be adopted without modifications in some form or other.
In consideration of such adaptations, a video camera system shown in FIG. 10 has been developed that makes the best use of the merits of the above-described two systems. This video camera includes a pitch sensor 100 for detecting the pitching of the main body of the video camera, a roll sensor 101 for detecting the rolling of the main body of the video camera, an active prism 102 that exhibits performance equivalent to the benefit achieved with a gimbal mechanical system but yet is reduced in size, a micro-computer 103 for driving and controlling the active prism 103 based on detection signals from the pitch sensor 100 and the roll sensor 101, and a CCD image sensor 104 for receiving an image pickup light radiated via the active prism 103 for generating image signals by photo-electric conversion.
The active prism 102 is formed of two round glass plates 102a, 102b interconnected by an expandable bellows 102c made of a special film material, and a liquid having the same refractive index as that of the glass plates 102a, 102b. The front glass plate 102a, on which the image pickup light falls, is provided with a transverse shaft 102d for deviating or tilting the front side glass plate 102a in the vertical or pitch direction, while the rear glass plate 102b, out of which the image pickup light is radiated, is provided with a vertical shaft 102e for deviating or tilting the front side glass plate 102b in the transverse or roll direction.
The shafts 102d, 102e are provided respectively with driving coils 105, 106 across which an electrical voltage may be applied for causing independent movements of the two glass plates 102a, 102b in accordance with the values of the applied voltage.
If the two glass plates 102a, 102b are parallel to each other, the active prism acts as a single glass plate, that is, it acts similarly to a system consisting of a transparent filter placed ahead of a lens, such that the image pickup light incident thereon is radiated directly without undergoing deflection.
If the main body of the camera is directed upward by the deviations caused by fine movements of the user's hand, the front side glass plate 102a is driven so as to be directed partially upward so that the optical axis of the image pickup light is deflected downward via the active prism 102. In this manner, the deviations of the camera caused by fine movements of the user's hand may be corrected over a wider range than with the picture processing system, without undergoing deterioration in resolution or fluctuations in the angle of the image field.
Meanwhile, the angle of inclination of the active prism 102 is typically set to be .+-.3.degree. at the maximum, for example, while the maximum range of correction of the deviations of the camera caused by fine movements of the user's hand, in terms of the angle of tilt of the optical axis, is .+-.1.5.degree..
In the operation of the above-described video camera, when the image pickup operation is started, the pitch sensor 100 and the roll sensor 101, acting as angular sensors, detect the deviations of the camera device caused by fine movements of the user's hand to generate a pitch detection signal and a roll detection signal, which are respectively supplied to an amplification circuit 107. The amplification circuit 107 amplifies the pitch detection signal and the roll detection signal and supplies the amplified signals to an A/D converter 108. The A/D converter 108 digitizes the pitch detection signal and the roll detection signal to form pitch detection data and roll detection data, which are respectively supplied to the micro-computer 103.
Because the pitch detection data and roll detection data are in the form of angular acceleration data, the micro-computer 103 performs an integrating operation on these data to form angle data. This enables detection of the angular changes of the camera caused by fine movements of the user's hand, that is, shaking of the camera.
The micro-computer 103 then checks if the angular change produced as the angular data has been caused by the deviations of the camera as a result of fine movements of the user's hand or has been caused by panning, which is transverse swinging of the video camera during imaging, or by tilting, which is vertical swinging of the video camera device during imaging.
Specifically, the micro-computer 103 determines that a large but slow angular change is being caused by panning/tilting, so that it is not responsive to such large, slow angular change.
If the micro-computer 103 determines that the angular change is being caused by deviations of the camera device as a result of fine movements of the user's hand, it detects an amount of the angle of correction from the angular data and forms two correction data, that is, correction data in both the pitch and roll directions, and transmits the correction data to a comparator 109.
The active prism 102 is controlled by inclination angle or tilt sensors 111, 112, provided on the front and back sides of the glass plates 102a, 102b, respectively. More specifically, the inclination angle sensors 111, 112 detect the inclination of the front and back side glass plates 102a, 102b of the active prism 102 to form front glass plate inclination detection data and back glass plate inclination detection data, which are supplied to the comparator 109. The comparator 109 compares the two correction data in the pitch and roll directions, supplied from micro-computer 103, to the front glass plate inclination detection data and back glass plate inclination detection data supplied from the inclination angle sensors 111, 112, respectively, and transmits comparison data to a driving coil driver 110.
The driving coil driver 110 is responsive to the comparison data to control the amount and the polarity of the current supplied to the driving coils 105, 106 that drive the front and back side glass plates 102a, 102b, respectively.
This causes the active prism 102 to be controlled such that it is inclined by an angle equivalent to the deviations of the camera device as a result of fine movements of the user's hand.
Consequently, the image pickup light L reflected from the image to be recorded, indicated by a broken line in FIG. 10, has its optical axis corrected by the active prism 102 by an amount corresponding to the deviations of the camera caused by fine movements of the user's hand and is radiated onto the CCD image sensor 104 via a zoom lens 113 for an enlarged size image pickup of the object.
In this manner, it is possible with the above-described video camera to correct the optical axis of the image pickup light by the active prism 102 in accordance with the deviations of the camera device caused by fine movements of the user's hand so that the image pickup light is corrected as to the optical axis that it is radiated on the CCD image sensor 104, thereby preventing the "wobbling" of the reproduced picture.
Nevertheless, the above-described shaking compensated video camera suffers from a problem in that because it makes use of the above-mentioned active prism 102 having the liquid of the same refractive index as that of the glass plates 102a, 102b charged into a space defined between these glass plates 102a, 102b, it is highly probable that air bubbles be generated in the liquid under a low atmospheric pressure, thereby rendering it impossible to effect accurate correction of the deviations of the camera device caused by fine movements of the user's hand.